Induction of plasminogen activator by UV light in normal and xeroderma pigmentosum fibroblasts.

Abstract

Normal and DNA repair-deficient human fibroblasts have been used to study induction of plasminogen activator (PA) by DNA damage. UV light induced the synthesis ofPA in skin fibroblasts of all types ofxeroderma pigmentosum (XP) in XP heterozygotes and in human amniotic cells. Enzyme induction was, however, not observed in fibroblasts of normal adults. In classical XP, which are deficient in excision repair, PA synthesis occurred in a narrow range of low-UV fluences. In such strains, the level of enzyme produced was correlated with the extent of repair deficiency. UVfluences required for PA induction in XP variants and XP heterozygotes were at least 10 times those inducing enzyme synthesis in excision-deficient XP. Maximum enzyme induction occurred 48 hr after irradiation, and the highest levels of enzyme produced were 15-20 times those of PA baseline levels. Electrophoretic analysis showed that UV irradiation enhances the synthesis ofthe Mr 60,000 human urokinase-type PA, which is present in low amounts in untreated cells. Our results suggest that PA induction in human cells is caused by unrepaired DNA damage and represents a eukaryotic SOS-like function. In addition, PA induction may provide a sensitive assay for detection of cellular DNA repair deficiencies and identification of XP heterozygotes. DNA damage induces in bacteria the coordinate expression of a set of diverse responses collectively called SOS functions. These functions include the appearance ofrepair and mutagenic activities, inhibition of septation, induction of certain prophages, and production of large amounts of the recA protein (for review, see ref. 1). Induction of SOS functions appears to involve the protease activity of the recA protein, which cleaves cellular repressors ofSOS functions including its own repressor, the lexA gene product (2-5).Several observations suggest that SOS-like activities are also (PA). PA is a highly specific serine protease closely associated with cellular transformation, neoplasia, and tumor promotion (for reviews, see refs. 16, 17). In view of the central role attributed to proteolysis in the regulation of SOS functions in bacteria and because of the possible relation of both PA and SOS-like functions with neoplastic transformation, we further explored the induction of PA in human cells by UV irradiation.In the present work, we studied the role of DNA repair in PA induction by skin fibroblasts from xeroderma pigmentosum (XP) patients. XP belongs to a class of repair-deficient human autosomal recessive disorders that have in common predisposition to cancer and chromosome instability (18,19). XP is clinically characterized by abnormally enhanced sensitivity to sunlight and the appearance of carcinomas in exposed areas of the skin. Two classes ofXP patients can be biochemically identified: those whose cells show defective excision repair of UV light-induced damage to DNA (excision-deficient XP) and patients whose cells are impaired in postreplication repair but exhibit normal excision repair (XP variants) ...

Molecular Mechanisms of Ultraviolet Radiation Carcinogenesis

“…UV radiation has been shown to induce plasminogen activator (Miskin and Ben-Ishai, 1981;Rotem et al, 1987), metallothionein and other genes (Angel et al, 1986) in human cells. Additionally, a number of biological effects such as stimulation of arachidonic acid release (DeLeo et al, 1985), up-regulation of histamine-stimulated prostaglandin E2 production, possibly through an increase in PKC levels (Steuer and Pentland, 1990), inhibition of epidermal growth factor binding (Furstenberger et al, 1981), and increased levels of the p53 cellular tumor antigen (Maltzman and Czyzyk, 1984) have been shown to occur in UV-treated cells.…”

Photoproducts in transcriptionally active DNA induce signal transduction to the delayed U.V.-responsive genes for collagenase and metallothionein

“…At the same time U.V. is absorbed by DNA, generating photoproducts which also result in transcription of genes and obviously in the activation of several transcription factors (Miskin and Ben-Ishai, 1981;Schorpp et al, 1984;Stein et al, 1989b;Lu and Lane, 1993;Yamaizumi and Sugano, 1994). One of the transcription factors, p53, is posttranslationally stabilized upon DNA damage (Maltzman and Czyzyk, 1984) probably requiring a protein modi®cation which inhibits p53 degradation and perhaps disturbs its association with Mdm2 (Kubbutat et al, 1997;Haupt et al, 1997).…”

Exposure of nondividing populations of primary human fibroblasts to UV (254 nm) radiation induces a transient enhancement in capacity to repair potentially lethal cellular damage.

“…A report of enhancement of post-replication repair by a low-dose UV-conditioning exposure (11) may also be interpreted (12) on the basis of the abnormal state of DNA replication at the time of the second exposure. Nevertheless, UV exposure of human fibroblasts has been shown to enhance levels of plasminogen activator (13) and DNA ligase (14), and agents that arrest DNA replication have been shown recently to induce synthesis of a nuclear membrane-bound protein in cell lines derived from B lymphocytes (15).…”